1. Field of Invention
The invention relates to an electronic control system, and especially to an electronic control system mounted on a vehicle, such as a motor vehicle, and used for detecting failures of various components of the vehicle.
2. Description of Related Art
It is well known that an electronic control system is used for controlling a variety of components of a vehicle such as a motor vehicle. The aforementioned vehicle includes the electronic control system that diagnoses failure of its own components as well as various components of the vehicle. For example, a known failure diagnosis of this kind, such as that performed by an electronic control system disclosed in Japanese Laid-open Patent Publication No. 2000-329874, is performed while an internal combustion engine of the vehicle is not operating, that is, the vehicle is in a stable state, such that accuracy of the diagnosis is improved. The electronic control system disclosed in the above publication includes a clock system that is supplied with power, not via an ignition switch, but directly from a power supply. The clock system is adapted to count the time for which the ignition switch has been OFF while the vehicle is not operating, and turn on a power supply circuit to supply power to and thereby start up the electronic control system when the counted time has reached a predetermined time.
According to the electronic control system disclosed in the above publication, however, when the electronic control unit has been started, a series of predetermined initial processes and various control process steps, such as the fuel injection control, are all performed based on the detection signals from the sensors, irrespective of whether the unit has been started by operating the ignition switch or by the clock system. The initial process steps include the turn-on controls for turning on engine-check lamps and monitors and so on. In this way, even when the electronic control unit has been started by the clock system, the same process steps as those performed when the unit has been started by operating the ignition switch are performed. That is, the series of predetermined initial process steps are all performed when the unit has been started by the clock system, in spite of the fact that it is only necessary at this time to operate the components related to the failure diagnosis. The power consumption increases, thus reducing the life of the in-vehicle battery.